In their simpler form, medical injection devices have comprised mechanically driven syringes wherein a clockwork mechanism, including a gear train, a mainspring, an escapement and a clutch, drives a syringe plunger. With such devices, fluid was preloaded into the syringe and delivered by injection to patients at controlled rates. An example of such devices is shown in U.S. Pat. No. 4,059,110.
Injection devices have also included electrical motors coupled to worm and spur gears for operating a spring driven syringe. An example of such devices is shown in U.S. Pat. No. 4,668,220. This type of device has been used primarily for controlling the delivery of preloaded fluid from a syringe to a patient over a long period of time.
Still others have incorporated features for electronically controlling the injection of preloaded fluid from a syringe to a patient. Such devices have electronically controlled the repeated delivery of partial amounts of fluid from a syringe, the time duration of the delivery, and the pressure of the fluid. Such devices have also been controlled so as to change the flow rates and pressures during the injection as desired, based on feedback information processed by computers.
In the above-described systems, the amount of fluid to be injected is preselected and loaded into the syringe. Thus, in existing devices the amount of fluid that can be injected at any one time, without reloading the syringe, is limited to the size of the syringe.
Apparatuses and methods for injecting oral contrast media into a patient through a nasogastric tube have been primarily limited to syringes operated by hand. For purposes of scanning selected organs or tissues by computed tomography ("CT") or by magnetic resonance imaging ("MRI"), oral contrast media is introduced into the patient's body in order to enhance the contrast of the particular organs or tissues to be viewed. Strict regulation of the rate of delivery of oral contrast media is particularly important so that the proper contrast and concentration of contrast fluid in the patient's body is achieved as prescribed by the attending physician for optimal viewing of the subject area and for acceptance of the contrast fluid by the patient's system. For example, in CT scans it has been found in practice that the desired concentration of oral contrast media is achieved by introducing the contrast fluid into the patient's nasogastric tube at a rate of one cup per ten minutes. Typically, the process of injection includes pre-loading a syringe with one cup of contrast fluid, injecting the same into the patient via a nasogastric tube, and repeating this process once every ten minutes until the desired amount of fluid is delivered. Of course, if a patient is conscious and able to swallow the contrast fluid, the desired concentration can be achieved by pouring a selected amount of fluid into a cup, bringing the cup to the patient's bedside, and repeating these tasks every ten minutes until the desired amount of fluid is transferred to the patient's system.
Oral contrast media typically contain barium or an iodinated contrast agent, both of which are difficult to ingest. If the oral contrast media is introduced to the patient's body at a rate faster than one cup per ten minutes, the patient is likely to reject the fluid from his or her body by vomiting.
Failure to adhere to a specified rate of delivery can also result in less than optimal viewing of the patient's internal organs through the scan. For instance, if delivered at a rate slower than that prescribed, or if vomited from the patient's body, a poor contrast may result due to the lower concentration of contrast fluid in the body.
Additionally, the likelihood for error in the manual delivery of oral contrast media to patients has been strong due to the human effort involved in measuring the amount of fluid to be delivered, in regulating the rate at which delivery is to occur, and in timing the repetitions of delivery. Where the patient is called upon to drink the fluid, or to monitor his or her own delivery of fluid, the possibility of error on the part of the patient is present as well as that of the nurse. The possibility for error on the part of the patient may be further increased depending on how the patient's judgment is effected by the injury or illness under which the patient is suffering. Likewise, the possibility for error on the part of the nurse is enhanced where the nurse is not able to devote full attention to the delivery of the fluid during the delivery period due to the number of patients he or she may be caring for, to the number of additional tasks he or she may be simultaneously performing, or to interruptions in the nurse's duties due to a more important matter arising such as an emergency situation concerning another patient. One example of such multiple tasks a nurse often performs simultaneously is the preparation of a patient for a CT or MRI scan, including achieving proper concentration of contrast media within the desired viewing area of the patient's body, while concurrently monitoring the progress of at least one other patient already prepared and undergoing a CT or MRI scan. The possibility of human error is also present when using known devices requiring manual pre-loading of fluid into syringes and manual timing of repeated injections.
Accordingly, it is seen that a need remains for an injection apparatus and method that periodically meters a selected amount of fluid from a reservoir rather than a syringe and injects that fluid into a patient at a desired rate repeating such metering and injecting as needed to transfer a desired amount of fluid to a patient. It is also seen that a need remains to reduce the possibility of human error caused by manually pre-loading, delivering, and timing repeated doses of oral contrast media to a patient at a desired rate. It is to the provision of such therefore that the present invention is primarily directed.